Porous carbon spheres from poly(4-ethylstyrene-co-divinylbenzene: role of ZnCl2 and KOH agents in affecting porosity, surface area and mechanical properties

Abstract

Abstract The synthesis of activated-porous carbon spheres, from a cross-linked polystyrene copolymer alone and in presence of different activating agents, such as ZnCl2 and/or KOH under thermal treatment at 800 °C, is reported. In this paper, the role of both the ZnCl2 and KOH not only as activating agents, but also as a hard template, is highlighted, which in addition avoid the collapse of the polymer spheres structure during the pyrolysis. It has been found that, while KOH favours the development of the microporosity and of the surface area, ZnCl2 promotes the mesoporous character of the carbon spheres. The focus of this work lies in the study of the effects of the combined use of ZnCl2 and KOH. The simultaneous presence of the two activating agents led to a general increment of the mesoporosity, even if the surface area resulted to be higher than that obtained via ZnCl2 alone activation and lower than in case of KOH alone. Structure, porosity and morphological properties of the samples have been characterized by X-ray diffraction, N2-physisorption, scanning electron and atomic force microscopies. As the spherical shape is associated to high performances, from the mechanical point of view, and being structural integrity a strategic factor for applications, the elastic modulus and the hardness of a selection of samples have been determined. The evaluation of the mechanical properties by nanoindentation, rarely used in this context for this kind of systems, was found to be crucial for foreseeing industrial applications and as an effective approach able to deal with micro-sized spheres and a relationship between surface area, porosity and mechanical properties has been discussed.